1. Field of the Invention
The present invention relates in general to transducers, and more particularly to underwater acoustic transducers. The present invention also relates to a transducer capable of radiating acoustic energy over a wide band of frequencies including very low frequencies and at deep depths. More particularly, the present invention relates to a multiply-resonant, piezoelectric-cantilever-type transducer mounted from a common stiff central rigid structure with the transducer operating in the bending mode and means for reducing dipole radiation cancellation effects.
2. Background Discussion
Low frequency underwater sound transducers require a large volume and compliant structure to obtain a low resonant frequency, such as 10 Hz, along with a high output level. This can be difficult to accomplish within a fixed volume at very low frequencies, even at shallow depths, and it becomes extremely challenging at deep depths where the hydrostatic pressure is high. That condition, coupled with a wide bandwidth, can be achieved with the present invention, which uses a fluid filled transducer of at least two cantilevers or one center mounted free edge disc with a common support structure. The disclosed “quad” cantilever resonant structure is similar to back-to-back tuning forks without stems providing one of the lowest flexural resonances for a given length and, because of the excitation of only the odd modes; there are no deep nulls between the modes of vibration providing a wide band response. Moreover, in accordance with the present invention the performance may be significantly improved by increasing the separation between opposite benders and replacing most of the enclosed fluid with silicone rubber. The silicone rubber may also be positioned and supported behind a dual cantilever bender pair or a single bender disc and provide significantly better performance than if replaced with a fluid such as water or the medium in which it is immersed. Although other materials such as cork with imbedded rubber or possibly paper may be considered, their compliant properties can be significantly compromised under pressure or as in the case of paper, be too stiff to cause an impedance miss-match between the bender and the fluid medium, typically water.